Unlike the process for approvals like UL, there are three routes to EMC compliance:
- Self-certification (89/ 336/EEC Article 10.1): Administratively, this is the simplest route, and may be achieved either with in-house testing or by a specialty test facility. The manufacturer declares that the products conform to the applicable harmonized European standards.
- Technical Construction File (TCF) (89/336/EEC Article 10.2): This requires a detailed record of drawings, specifications, design details, and full information to enable vetting by the authorities. The TCF should enable a competent body (usually an accredited laboratory) to vet the design and confirm that it would comply if retested independently. This route is used when the manufacturer has not applied the harmonized standards, or has applied them only in part, or applied them in the absence of relevant standards.
- EC-type examination by a notified body (89/336/EEC Article 10.5): This specialized route is applicable only to radio communications equipment.
The costs involved in using external services have led many companies to invest in in-house facilities to undertake so-called precompliance testing (see the figure). Work is done in-house until the company believes that a product will pass the first time in compliance testing.
The facilities required for precompliance testing are less stringent, and are therefore, less expensive than full testing. Nonetheless, they allow engineers to more easily make the iterative design changes often required to reduce EMC problems. As usual, however, it is better to design out as many problems as possible from the beginning.
Even though a dc-to-dc converter is outside the LVD voltage range, and does not require CE marking, any equipment into which it is built will need to comply with the EMC Directive. Therefore, it is essential that the module be designed with the regulations in mind. In fact, designing converters to have low emissions and low susceptibility is critical to meeting the short time-to-market window many designers are facing. Allowing designers to meet this window is one of the major benefits of using on-board dc-to-dc converters.
EMC is becoming almost an industry in its own right, and considering the power supply's place between the line and the equipment, the supply has a key role to play. Although the performance is determined more by the layout of the equipment than by the supply itself, a few tips can enhance the advantage of using on-board dc-to-dc converters.
Using converters with built-in radio-frequency-interference filtering will minimize the disturbance on the supply lines. Practical experience shows that in order for the final equipment to meet the typical requirement of EN55022 class B, the converter must be designed with EMC control in mind, ideally meeting EN55022 class A. This sort of performance is only possible with LC-type filtering in the power module. Check the specification first.
When planning decoupling, the goal is to minimize path length and loop area. Dc-to-dc converters offer a significant intrinsic ability to decouple fast transients close to the load, minimizing the antenna effect of long supply lines. Keep any additional output filtering below 100 µF/A to avoid longer settling times and reduced stability.
A number of smaller-value capacitors, evenly distributed around the board, will be more effective than a single component, especially for the high-frequency decoupling. Don't forget that while parallel capacitors are additive, parallel resistance and inductance reduce, providing a double gain in the time constant.
An earth or ground plane in the printed-wiring board will not only provide some screening, but improve the EMC performance. It does this by introducing distributed decoupling capacitance for the highest frequencies, and reducing the inductance in both the ground path and signal distribution.
Surface mounting offers significant benefits in terms of reduced lead inductance and high-frequency radiation from the leads and traces. With surface-mount dc-to-dc converters now available that can handle up to 15 W, this is an increasingly practical and effective option.
The SLIM Initiative And EMC
The European Commission has recognized the complexity of the legislation that has established the Single Market, and in May 1996, it embarked on a program of simplification known as the Simpler Legislation for the Single Market (SLIM). The activity is planned to be completed in phases, with the EMC legislation coming under attention in phase III.
The SLIM team's report is expected to be presented by the end of the year, complete with conclusions and recommendations, which it is hoped will streamline and reinforce the Single Market concept.
In closing, please remember that the EU legislation has teeth. Equipment found to contravene the EMC Directive can be seized and banned from sale throughout the EU. In addition, the penalties for knowingly supplying or CE marking non-compliant equipment include fines and imprisonment.
Unlike the process for approvals like UL, there are three routes to EMC compliance:
- Self-certification (89/ 336/EEC Article 10.1): Administratively, this is the simplest route, and may be achieved either with in-house testing or by a specialty test facility. The manufacturer declares that the products conform to the applicable harmonized European standards.
- Technical Construction File (TCF) (89/336/EEC Article 10.2): This requires a detailed record of drawings, specifications, design details, and full information to enable vetting by the authorities. The TCF should enable a competent body (usually an accredited laboratory) to vet the design and confirm that it would comply if retested independently. This route is used when the manufacturer has not applied the harmonized standards, or has applied them only in part, or applied them in the absence of relevant standards.
- EC-type examination by a notified body (89/336/EEC Article 10.5): This specialized route is applicable only to radio communications equipment.
The costs involved in using external services have led many companies to invest in in-house facilities to undertake so-called precompliance testing (see the figure). Work is done in-house until the company believes that a product will pass the first time in compliance testing.
The facilities required for precompliance testing are less stringent, and are therefore, less expensive than full testing. Nonetheless, they allow engineers to more easily make the iterative design changes often required to reduce EMC problems. As usual, however, it is better to design out as many problems as possible from the beginning.
Even though a dc-to-dc converter is outside the LVD voltage range, and does not require CE marking, any equipment into which it is built will need to comply with the EMC Directive. Therefore, it is essential that the module be designed with the regulations in mind. In fact, designing converters to have low emissions and low susceptibility is critical to meeting the short time-to-market window many designers are facing. Allowing designers to meet this window is one of the major benefits of using on-board dc-to-dc converters.
EMC is becoming almost an industry in its own right, and considering the power supply's place between the line and the equipment, the supply has a key role to play. Although the performance is determined more by the layout of the equipment than by the supply itself, a few tips can enhance the advantage of using on-board dc-to-dc converters.
Using converters with built-in radio-frequency-interference filtering will minimize the disturbance on the supply lines. Practical experience shows that in order for the final equipment to meet the typical requirement of EN55022 class B, the converter must be designed with EMC control in mind, ideally meeting EN55022 class A. This sort of performance is only possible with LC-type filtering in the power module. Check the specification first.
When planning decoupling, the goal is to minimize path length and loop area. Dc-to-dc converters offer a significant intrinsic ability to decouple fast transients close to the load, minimizing the antenna effect of long supply lines. Keep any additional output filtering below 100 µF/A to avoid longer settling times and reduced stability.
A number of smaller-value capacitors, evenly distributed around the board, will be more effective than a single component, especially for the high-frequency decoupling. Don't forget that while parallel capacitors are additive, parallel resistance and inductance reduce, providing a double gain in the time constant.
An earth or ground plane in the printed-wiring board will not only provide some screening, but improve the EMC performance. It does this by introducing distributed decoupling capacitance for the highest frequencies, and reducing the inductance in both the ground path and signal distribution.
Surface mounting offers significant benefits in terms of reduced lead inductance and high-frequency radiation from the leads and traces. With surface-mount dc-to-dc converters now available that can handle up to 15 W, this is an increasingly practical and effective option.
The SLIM Initiative And EMC
The European Commission has recognized the complexity of the legislation that has established the Single Market, and in May 1996, it embarked on a program of simplification known as the Simpler Legislation for the Single Market (SLIM). The activity is planned to be completed in phases, with the EMC legislation coming under attention in phase III.
The SLIM team's report is expected to be presented by the end of the year, complete with conclusions and recommendations, which it is hoped will streamline and reinforce the Single Market concept.
In closing, please remember that the EU legislation has teeth. Equipment found to contravene the EMC Directive can be seized and banned from sale throughout the EU. In addition, the penalties for knowingly supplying or CE marking non-compliant equipment include fines and imprisonment.